Processing of liquids, such as aspiration and dispensation, is carried out in a variety of contexts. For example, in a laboratory setting, a robotic device may aspirate and dispense liquids using a positive-displacement pump and associated pipette tip in order to carry out a variety of laboratory tasks, such as titration for performing a DNA assay. In such settings, it may be advantageous to detect when the pipette tip comes into and out of contact with the liquid being aspirated or dispensed. However, conventional liquid level detection methods and apparatuses suffer from a lack of sensitivity, which can result in inaccuracies when aspirating and dispensing small volumes (e.g., microliters) of liquid, a poor ability to accurately confirm whether the pipette tip has fallen out of the liquid during aspiration, and/or a poor ability to confirm that the proper downward motion of the pipette tip has occurred to compensate for a height reduction of a liquid sample resulting from a previous aspiration.